You can mark August 26, 2012, as the date that the record low was set for Arctic sea ice extent. That’s a good six weeks before the usual mid-September end of what in this context is called the “melt season.”

Picture for a moment the state of Indiana, all 32,000 square miles (89,200 sq km) of it. That helps create a mental image of the area of sea ice currently being lost each year. Repeat: We’re losing about one Indiana each year, a statement that might excite some other Big 10 basketball powerhouses … but few others.

Overall, the Arctic, since 1980, has lost about 50 percent of its summer ice cover. Arctic sea ice extents in the past six Septembers are the lowest since satellite record-keeping got under way in 1979.

To better wrap one’s mind around the scope of these numbers, picture now a map of the 48 continental states, but not including Arizona. Those 47 continental U.S. states, again minus Arizona, would be comparable to the September areas of the Arctic covered by sea ice about three decades ago. The map below, drawn from the PowerPoint presentation used in the webinar, illustrates the point: All but Arizona were under ice.

Looking at the map below of the contiguous states, only the area to the west of the western borders of the Dakotas, Iowa, Missouri, Arkansas, and Louisiana are today covered by Arctic sea ice. The whole eastern half of the continental U.S. — the Dakotas, Iowa, Missouri, Arkansas, and Louisiana and all points east — would represent the area now lacking sea ice.

To put it another way, there currently is about 1.3 million square miles (3.5 million square kilometers) of Arctic sea ice. That compares with the previous recorded low, in 2007, of about 1.6 million square miles (4.17 million square kilometers). And that compares with the approximately 2.7 million square miles (7 million square kilometers) that we used to think of as average.

It’s not just sea ice extent that is being lost, according to scientist Walt Meier, of the National Snow and Ice Data Center in Boulder, Co. It’s volume too. He pointed to some inevitable uncertainties involved in model estimates and how they are arrived at, but said the usual 12,000 cubic kilometers of Arctic sea ice appears to be heading toward a total closer to 5,000 cubic kilometers.

“Vast areas are first-year ice,” Meier said in the September 12 webinar aimed at improving public understanding of and communications on climate change issues. He explained that age of ice is a proxy for estimating sea ice thickness. “Other things being equal: Older ice = Thicker ice,” one of his slides emphasized. And data clearly indicate a smaller proportion of old ice in the Arctic. There’s evidence too that the declining amount of summer-time old ice is the result of melting, and not of its simply drifting off into more wide-open waters.

An Ice-Free Arctic Summer Month? A Matter of When … Not If

It’s a matter of when, and not whether, we’ll have ice-free Arctic summer months, Meier explained. He said observed declines exceed what IPCC in 2007 had officially forecast would be occurring.

“Things are moving very quickly, and much more quickly than IPCC had forecast,” said Meier, who himself had been an active participant in that most recent IPCC report. He said there is a lot of uncertainty involved in estimating just when that “ice-free Arctic” could occur, but he said the period between 2030 and 2050 could be a reasonable estimate at this point.

As for impacts across North America of continued record-low Arctic sea ice extents, Meier in his presentation referred to impacts on local communities, on shipping and navigation and resource extraction, on tourism, on national sovereignty and defense issues, and on global climate impacts. Some impacts, he noted, will be positive, and others not.

He emphasized that the continuing loss of summer sea ice decreases albedo: With sea ice, at least 60 percent of the Sun’s energy is reflected back into the space, and without it only about 10 percent. With the dark ocean area absorbing more of the Sun’s energy during summer months than the light sea ice would, the rising ocean heat and temperatures help warm the atmosphere into fall … the so-called “Arctic Amplification.”

In addition, less sea ice means more transfer of moisture to the atmosphere … and therefore more water vapor in autumn, again amplifying warming.

Among the likely results? Changing storm tracks and precipitation patterns. Most of the U.S., and in particular out west, becomes drier with less Arctic summer sea ice.

Meier’s bottom line, or take-home message … at least one of them: “I like to say the Arctic isn’t Las Vegas,” he concluded. “What happens in the Arctic doesn’t stay in the Arctic.”

The PowerPoint presentation Meier used in his webinar — one version of it including a well-worthwhile animation of the shrinking ice extent and another without that animation — is available online. The file with the animation is about 100 megabytes, and the file without about 16 megabytes. If your network access is fast enough and your curiosity piqued, the animation makes for a compelling message.